The problem with PE waste is entirely getting it to one place. If that can be done, it can easily be managed. Pure PE "waste" would be a resource if collected in one place in sufficient quantity reproducibly. Any polymer is a bunch of molecules strung together, and above a certain temperature they will dissociate (ceiling temperature) if initiated. Just as the small "mers" will join (polymerize), so they will also disjoin (depolymerize) back into the "mers".
And the stuff can be burned for energy if collected in a near pure state. Collection however is an issue. The bodies of milk jogs are PE, the cap however is PP.
We in the US collect "recyclables" mixed all together, and about the only thing pulled out of that stream is aluminum, the rest goes to landfill.